Device for controlling an operating characteristic of an internal combustion engine

ABSTRACT

A device for controlling an operating characteristic of an internal combustion engine is suggested with a speed limitation being effective according to a predetermined time function by influencing the fuel metering during the transition from the idling state to the driving mode. This speed limitation is activated especially in the event of a fault of the actuating device, of its activation and of the feedback and in the event of a speed response critical to safety in the idling state.

FIELD OF THE INVENTION

The invention relates to a device for controlling an operatingcharacteristics of an internal combustion engine.

BACKGROUND OF THE INVENTION

A device of this type for controlling an operating characteristic of aninternal combustion engine is known from U.S. Pat. No. 4,635,607. There,a fuel-metering system is presented with an actuator for influencing thesupply of air to the internal combustion engine, with means which detecta driving condition critical to safety by checking the drive signal ofthe air-influencing actuator with respect to limit values. Furthermore,this means detects a fluctuation of the idling speed by checking thespeed as a function of time and the means also, in the presence of adriving condition critical to safety, modifies the condition for fuelcut-off in such a way that, increasing linearly as a function of speed,this condition is still valid for openings of the throttle flap of up to5°.

Moreover, it is known from U.S. Pat. No. 4,311,123 to increase the fuelquantity according to a selectable time function by opening the idlingcontact after deceleration has ended. This allows a smooth transition tothe normal driving mode.

Furthermore, it is known from U.S. Pat. No. 4,305,359 to detect a defectof the actuator for guidance control by checking the actuator positionand accelerator-pedal position. A defect is assumed when the acceleratorpedal is in the idling position and the actuator, especially thethrottle flap, is outside its idling position. When such a defect ispresent, the fuel supply is cut off in order to reduce the speed. Whenthe driver moves the accelerator pedal out of its idling position again,the cut-off of the fuel supply is cancelled in order to avoid drivingconditions critical to safety. The speed of the internal combustionengine can thereby be increased again.

However, it is a disadvantage that, when the throttle is opened, thesudden torque jump can give rise to an undesirable vehicle acceleration,with the result that the driver is possibly no longer in control of thesituation.

It is the object of the invention to improve the driving performanceduring the transition from the idling mode to the driving mode in adevice for controlling an operating parameter of an internal combustionengine of the type mentioned above and to prevent driving conditionscritical to safety.

Furthermore, a method for controlling the fuel-metering system of aninternal combustion engine in the overrun mode is known from U.S. Pat.No. 4,549,519. There, the actual speed is compared with a predeterminedspeed threshold value which is reduced from a high initial value to alow final value according to a time function. If the actual speed isabove this speed threshold, the fuel supply is cut off. Conversely, whenthe speed is lower than this speed threshold value, the fuel supplyresumes. The transition from the overrun mode to the normal operatingstate is not described herein.

In the following, the term "idling state" covers all the operatingstates in which the accelerator pedal or throttle flap are in theiridling position, especially the overrun mode.

SUMMARY OF THE INVENTION

The device according to the invention improves the driving performanceof an internal combustion engine in the event of a defective state ofthe actuator controlling the air throughput, of its activating devicesand lines and of its feedback devices and lines during the transitionfrom the idling state to the normal driving mode by controlling a speedlimitation by fuel cut-off according to a predetermined time function. Atorque jump which could be critical to safety and which can occur underspecific operating conditions, is effectively prevented.

In particular, in the above-mentioned event of a defect, the deviceaccording to the invention is capable of overcoming driving conditionscritical to safety and of maintaining a reliable operation of theinternal combustion engine. The invention starts from the fact that, inthe event of a defect, a driving condition critical to safety is to beexpected only when, in the idling state, the speed oscillates about thepredetermined speed threshold value for the fuel cut-off.

Furthermore, the device according to the invention can also be usedother than when a defect is present, especially after the overrun modeof operation. Fuel cut-off also means the elimination of individualinjection pulses.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained below with reference to the embodiment shownin the drawings.

FIG. 1 shows a schematic representation of the device according to theinvention, and

FIG. 2 shows possible speed responses with the occurrence of theabove-described defects and an effective fuel cut-off above a speedthreshold. FIGS. 3a and 3b represent a possible response of the speedlimitation as a function of the position of the throttle flap or of theaccelerator pedal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows an internal combustion engine 10 with at least onefuel-injection valve 11 and an intake pipe 12, in which a throttle flap13 with a throttle-flap position transducer 13a, an actuating device 14setting the throttle flap and an idling switch 14a are located. Theillustrated device also has a speed sensor 17 and a position transducer18 of an accelerator pedal 19 which controls the throttle flap 13 and towhich a switch for the zero position of the accelerator pedal isassigned. A control unit 20 receives via its input 31 the actual speedfrom the speed sensor 17, via its input 33 the idling signal and via itsinput 34 the throttle-flap position from the throttle-flap positiontransducer 13a. The idling signal can be picked up either from theidling switch 14a or from the accelerator-pedal position transducer 18,as represented symbolically in FIG. 1 by the switch unit 53. The input33 of the control unit 20 is connected to these transducers 14a and 18via the switch unit 53.

Via outputs 36 and 37 of the control unit 20, the operatingcharacteristic fuel quantity is controlled via a correspondingactivation for at least one injection valve 11 and the operatingcharacteristic idling air-throughput is controlled via the actuatingdevice 14 of the throttle flap 13.

The control unit 20 consists essentially of a device 40 for detecting adriving condition critical to safety, of a fault detection circuit 41,of a computation unit for the fuel quantity 42, of a device 43 fordetermining the speed threshold value for the fuel cut-off and of acomputation unit 44 for actuating the adjusting device 14. These devicesare assigned to individual regions of the control unit.

The input signals of the device 40 for detecting a driving statecritical to safety are the engine speed and a speed threshold valuepredetermined via the feed line 50. Furthermore, the device 40 isconnected to a timer 51. The output of this device 40 is connected viaan AND-logic element 52 to the device 43 for forming the speed limitingvalue. The second input of the AND-logic element 52 receives the idlingsignal via the input 33.

The fault detection circuit 41 processes as input signals the idlingsignal, the output signal of the computation unit 44 and thethrottle-flap position. Its single output is connected to the device 43for forming the speed limiting value and, via an AND-logic element 51alinked to the idling signal, to the timer 51. In addition to theabove-described input signals, the device 43 has via a feed line 54 afurther input signal which considers various operating conditions of theinternal combustion engine. The output of the device 43 is connected toan AND-logic element 56 via a comparator device 55. The second input ofthe comparator device 55 receives the speed signal from the input 31.The speed and throttle-flap position are supplied to the computationunit 42 for the fuel-metering signal and the output of the computationunit 42 is connected to the second input of the AND-logic element 56.The feed line 57 of the computation unit 42 represents further operatingcharacteristics which are required for computing the fuel-meteringsignal. By these are meant especially the temperature and theexhaust-gas composition. The computation unit 44 forms the activatingsignal for the actuating device 14 from the idling signal and speed.Further operating characteristics, such as are known from idlingcontrols, are fed to the computation unit 44 via a feed line 58. Theoutput of the AND-logic element 56 is connected to the output 36 of thecontrol unit 20 and therefore to the fuel valve 11 of the internalcombustion engine, and the output of the computation unit 44 isconnected to the adjusting device 14 via the output 37 of the controlunit 20.

The device 40 is activated by the fault detection circuit 41 and by theidling signal from the input 33 and checks the speed trend of theinternal combustion engine by comparing the speed with a predeterminedthreshold value. During predetermined time intervals determined by thetimer 51, the device 40 detects from the results of the comparisonwhether there are speeds higher and lower than the speed thresholdvalue. If the internal combustion engine is in the idling state which istaken into account by the logic element 52 and which uses the idlingsignal as a second input variable, then the device 43 for determiningthe speed limiting value is addressed according to the result of thecheck of the speed response in the device 40.

The fault detection circuit 41 detects abnormal operating states as afunction of the throttle-flap position, the magnitude of the activatingsignal for the actuating device 14 and the idling signal. Thethrottle-flap position is compared with a computed desired value. It isthus possible to consider all the faults in which the opening of theair-throughput actuator 13 can no longer be reduced and thereforeremains inadmissibly large. When a fault is detected, the faultdetection circuit 41 activates the device 43 for forming the speedlimiting value and, via the AND-logic element 51a and the timer 51, thedevice 40.

FIG. 2 shows the possible speed responses in the idling state of theinternal combustion engine in the event of a fault. The predeterminedspeed value, designated by n_(o) in FIG. 2 and fed to the device 40 viathe feed line 50, is selected high enough to ensure that it is above thenormal speed. As shown in FIG. 2a, the speed can constantly be below thespeed threshold value 50 during the time interval predetermined by thetimer 51. In this case, the detected fault does not have a seriouseffect on the speed, that is, the opening of the actuator 13 is, forexample, not inadmissibly wide, or the engine is subjected to a highload by mechanical or electrical consumers. No behavior critical tosafety is therefore to be expected during the transition from the idlingstate into another operating state of the internal combustion engine. Inthis case, the device 43 is consequently cut off outside the idlingstate. In FIG. 2b, the speed is constantly higher than the speedthreshold value. From this speed response with a fuel cut-off it isconcluded that the vehicle is in the overrun mode. Here too, the device43 according to the invention is not active outside the idling state,since an immediate take-up without an interruption of torque isdesirable. Because of the fuel cut-off above the speed threshold thereis therefore a driving condition critical to safety only when, as shownin FIG. 2c, the speed oscillates about the speed threshold value. Inthis case, the device 43 according to the invention must supply a speedlimiting value even outside the idling state. The device 43 thereforetransmits a speed limiting value with the opening of the idling switchwhen, in the idling state, there is a fault detection signal from thecircuit 41 and the device 40 has additionally detected an oscillation ofthe speed about the speed threshold value 50.

FIG. 3b shows the trend of the speed limiting value in and outside theidling state when the last-mentioned case occurs. Thus, if the idlingswitch is opened at the time t_(o) or the accelerator pedal shifted, asin FIG. 3a, then the device 43 increases the speed limiting valueslightly and raises it according to a time function. A limit valuedetermines the maximum speed limiting value. In FIG. 3b, a ramp functionis shown as a time function.

The comparator device 55 constantly compares the speed limiting valuewith the speed and cuts off the fuel supply via the logic element 56when the speed is higher than the speed limiting value and cuts in thefuel when the speed falls below the speed limiting value.

Advantageous other embodiments of the device according to the inventionare described below.

Besides the embodiment shown in FIG. 1, which was chosed merely for thesake of clarity, the procedure described can also be carried out in acomputer.

In order to extend the fault detection, an air-mass meter 60 can be usedadditionally in the device according to the invention. This air-massmeter 60 transmits an air-mass signal 61 to the fault detection circuit41 and to the computation unit 42 for fuel metering. Moreover, the speedsignal can also be processed for fault detection.

Furthermore, instead of one speed threshold value, it is possible topredetermine two separate speed threshold values with an intermediatespeed band for fuel cut-off and cut-in. Speed oscillation is detectedwhen speed values occur above and below this speed band.

Moreover, speed oscillation can be determined by detecting alternatelypositive and negative speed gradients as a function of a predeterminedlimit value and of a predetermined speed.

Of course, the time function for raising the speed limiting value is notrestricted to the ramp function described in the exemplary embodiment.Thus, any time function can be realized in dependence on the operatingstates of the internal combustion engine. In particular, this timefunction can be dependent on parameters such as the actuating speed ofthe accelerator pedal or of the throttle flap, or on the driving speed.In FIG. 1, this is taken into account by the additional input 54 of thedevice 43 for determining the speed limiting value. A dependence of thisspeed limiting value on the actuating speed of the accelerator pedalmeans that, even in the event of a fault, the internal combustion enginereacts to the driver's wishes outside the idling state.

In an extension of the exemplary embodiment, in the event of a fault,the check of the speed response is independent of the position of theidling switch 14a.

Moreover, a general presetting of a minimum reinjection speed and amaximum cut-off speed can ensure that emergency operation is limited toa speed band predetermined thereby.

Of course, the device according to the invention also includes thecontrol of an operating characteristic of an internal combustion enginewith a bypass channel and an adjusting device controlling the airthroughput in this bypass channel.

The device according to the invention can also be used analogously afterthe overrun mode in a way corresponding to the above exemplaryembodiment.

Furthermore, the idling signal can also be picked up directly from thethrottle-flap position transducer 13a.

In summary, it is found that the device described first detects thefault, then activates the speed limiting value n_(o) in the idling stateand thereafter checks for a driving condition critical to safety. Ifthis check is positive, according to the invention the speed limitationis increased during the transition from the idling state or overrun modeto the driving mode.

We claim:
 1. An arrangement for controlling an operating parameter of aninternal combustion engine having an air-intake pipe, the arrangementcomprising:actuating means for adjusting the air through-put passing tothe engine through said intake pipe with said actuating means beingadjustable to correspond to an idle condition of the engine and a drivecondition of the engine; idle-condition detection means for detectingthe adjustment of said actuating means corresponding to said idlecondition; control means for controlling the fuel metered to the engine;drive-condition detection means for detecting a drive condition criticalto safety produced by a fault in said actuating means for adjusting theair flow to the engine during idle; engine speed limiting meansoperatively connected to said control means and being actuable by saiddrive-condition detection means for limiting the speed of the engine;and, said engine speed limiting means being effective in said idlecondition and said drive condition and being adapted to emit an enginespeed limit value increasing as a function of time as the engine passesfrom said idle condition to said drive condition.
 2. The arrangement ofclaim 1, wherein said drive-condition detection means checks the enginespeed response in said idle condition and activates said engine speedlimiting means in both said idle condition and said drive condition inresponse to an oscillation of the engine speed.
 3. The arrangement ofclaim 1, wherein the engine speed limit value follows a pregiven timefunction when the accelerator pedal or the throttle flap is actuated. 4.The arrangement of claim 3, wherein said time function is a rampfunction.
 5. The arrangement of claim 1, wherein said drive-conditiondetection means checks the engine speed response independently of theidle condition after a fault detection.
 6. An arrangement forcontrolling an operating parameter of an internal combustion enginehaving an air-intake pipe, the arrangement comprising:actuating meansfor adjusting the air through-put passing to the engine through saidintake pipe with said actuating means being adjustable to correspond toan idle condition of the engine and a drive condition of the engine;idle-condition detection means for detecting the adjustment of saidactuating means corresponding to said idle condition; control means forcontrolling the fuel metered to the engine; drive-condition detectionmeans for detecting a drive condition critical to safety; engine speedlimiting means operatively connected to said control means and beingactuable by said drive-condition detection means for limiting the speedof the engine; said engine speed limiting means being effective in saididle condition and said drive condition and being adapted to emit anengine speed limit value increasing as a function of time as the enginepasses from said idle condition to said drive condition; and, means fordetecting a fault of said actuating means influencing the airthroughput, and detecting the drive of said actuating means or thefeedback of said actuating means in the idle condition and said enginespeed limiting means being effective as a function of this fault.
 7. Thearrangement of claim 6, wherein a fault is detected by a check of thethrottle-flap position in the idle condition with a plausibilitycomparison between actual value and activating value being carried out.8. The arrangement of claim 7, wherein an air-mass measurement signal oran engine speed signal is additionally processed for fault detection andis included in the plausibility check.
 9. An arrangement for controllingan operating parameter of an internal combustion engine having anair-intake pipe, the arrangement comprising:actuating means foradjusting the air through-put passing to the engine through said intakepipe with said actuating means being adjustable to correspond to an idlecondition of the engine and a drive condition of the engine;idle-condition detection means for detecting the adjustment of saidactuating means corresponding to said idle condition; control means forcontrolling the fuel metered to the engine; drive-condition detectionmeans for detecting a drive condition critical to safety; engine speedlimiting means operatively connected to said control means and beingactuable by said drive-condition detection means for limiting the speedof the engine; said engine speed limiting means being effective in saididle condition and said drive condition and being adapted to emit anengine speed limit value increasing as a function of time as the enginepasses from said idle condition to said drive condition; and, comparatormeans for detecting an oscillation of the engine speed by successivecomparisons of the actual engine speed (n) with a predeterminedthreshold value (n_(t)).
 10. The arrangement of claim 9, whereindrive-condition detection means are adapted to check the speed responseduring predetermined time intervals.
 11. The arrangement of claim 9,wherein said oscillation of the engine speed is detected by alternatingspeed gradients as a function of a limit value and of a pregiven enginespeed.
 12. The arrangement of claim 9, wherein the speed threshold valueis configured as a speed band with a higher cut-off speed and a lowerresumption speed.
 13. An arrangement for controlling an operatingparameter of an internal combustion engine having an air-intake pipe,the arrangement comprising:actuating means for adjusting the airthrough-put passing to the engine through said intake pipe with saidactuating means being adjustable to correspond to an idle condition ofthe engine and a drive condition of the engine; idle-condition detectionmeans for detecting the adjustment of said actuating means correspondingto said idle condition; control means for controlling the fuel meteredto the engine; drive-condition detection means for detecting a drivecondition critical to safety; engine speed limiting means operativelyconnected to said control means and being actuable by saiddrive-condition detection means for limiting the speed of the engine;said engine speed limiting means being effective in said idle conditionand said drive condition and being adapted to emit an engine speed limitvalue increasing as a function of time as the engine passes from saididle condition to said drive condition; and, said engine speed limitvalue following a pregiven time function when the accelerator pedal orthe throttle flap is actuated and said engine speed limit value assumingdifferent responses in dependence on the actuating speed of theaccelerator pedal, on the throttle flap or on the driving speed of thevehicle.